AP-42, CH 9.2.2: Pesticide Application

9.2.2PesticideApplication 9.2.2.1General1-2 Pesticidesaresubstancesormixturesusedtocontrolplantandanimallifeforthepurposesof increasingandimprovingagriculturalproduction,protectingpublichealthfrompest-bornediseaseand discomfort,reducingpropertydamagecausedbypests,andimprovingtheaestheticqualityofoutdoor orindoorsurroundings.Pesticidesareusedwidelyinagriculture,byhomeowners,byindustry,andby governmentagencies.Thelargestusageofchemicalswithpesticidalactivity,byweightof"active ingredient"(AI),isinagriculture.Agriculturalpesticidesareusedforcost-effectivecontrolofweeds, insects,mites,fungi,nematodes,andotherthreatstotheyield,quality,orsafetyoffood.Theannual U.S.usageofpesticideAIs(i.e.,insecticides,herbicides,andfungicides)isover800millionpounds. AiremissionsfrompesticideusearisebecauseofthevolatilenatureofmanyAIs,solvents, andotheradditivesusedinformulations,andofthedustynatureofsomeformulations.Mostmodern pesticidesareorganiccompounds.EmissionscanresultdirectlyduringapplicationorastheAIor solventvolatilizesovertimefromsoilandvegetation.Thisdiscussionwillfocusonemissionfactors forvolatilization.Thereareinsufficientdataavailableonparticulateemissionstopermitemission factordevelopment. 9.2.2.2ProcessDescription3-6 ApplicationMethods- Pesticideapplicationmethodsvaryaccordingtothetargetpestandtothecroporothervalue tobeprotected.Insomecases,thepesticideisapplieddirectlytothepest,andinotherstothehost plant.Instillothers,itisusedonthesoilorinanenclosedairspace.Pesticidemanufacturershave developedvariousformulationsofAIstomeetboththepestcontrolneedsandthepreferred applicationmethods(oravailableequipment)ofusers.Thetypesofformulationsaredry,liquid,and aerosol. Dryformulationscanbedusts,granules,wettableandsolublepowders,waterdispersible granules,orbaits.Dustscontainsmallparticlesandaresubjecttowinddrift.Dustsalsomaypresent anefficacyproblemiftheydonotremainonthetargetplantsurfaces.Granularformulationsare larger,fromabout100to2,500micrometers(µm),andareusuallyintendedforsoilapplication. Wettablepowdersandwater-dispersiblegranulesbothformsuspensionswhenmixedwithwaterbefore application.Baits,whichareaboutthesamesizeasgranules,containtheAImixedwithafood sourceforthetargetpest(e.g.,branorsawdust). Liquidformulationsmaybesolutions,emulsions(emulsifiableconcentrates),aerosols,or fumigants.Inaliquidsolution,theAIissolubilizedineitherwaterororganicsolvent.Truesolutions areformedwhenmiscibleliquidsorsolublepowdersaredissolvedineitherwaterororganicliquids. EmulsifiableconcentratesaremadeupoftheAI,anorganicsolvent,andanemulsifier,whichpermits thepesticidetobemixedwithwaterinthefield.AflowableformulationcontainsanAIthatisnot amenabletotheformationofasolution.Therefore,theAIismixedwithaliquidpetroleumbaseand emulsifierstomakeacreamyorpowderysuspensionthatcanbereadilyfield-mixedwithwater. Aerosols,whichareliquidswithanAIinsolutionwithasolventandapropellant,areusedfor fogormistapplications.Therangesofoptimumdropletsize,bytarget,are10to50µmforflying 1/95 FoodAndAgriculturalIndustries 9.2.2-1 insects, 30 to 50 µm for foliage insects, 40 to 100 µm for foliage, and 250 to 500 µm for soil with drift avoidance. Herbicides are usually applied as granules to the surface of the soil or are incorporated into the soil for field crops, but are applied directly to plant foliage to control brush and noxious weeds. Dusts or fine aerosols are often used for insecticides but not for herbicides. Fumigant use is limited to confined spaces. Some fumigants are soil-injected, and then sealed below the soil surface with a plastic sheeting cover to minimize vapor loss. Several types of pesticide application equipment are used, including liquid pumps (manual and power operated), liquid atomizers (hydraulic energy, gaseous energy, and centrifugal energy), dry application, and soil application (liquid injection application). 9.2.2.3 Emissions And Controls1,7-14 Organic compounds and particulate matter are the principal air emissions from pesticide application. The active ingredients of most types of synthetic pesticides used in agriculture have some degree of volatility. Most are considered to be essentially nonvolatile or semivolatile organic compounds (SVOC) for analytical purposes, but a few are volatile (e. g., fumigants). Many widely used pesticide formulations are liquids and emulsifiable concentrates, which contain volatile organic solvents (e. g., xylene), emulsifiers, diluents, and other organics. In this discussion, all organics other than the AI that are liquid under ambient conditions, are considered to have the potential to volatilize from the formulation. Particulate matter emissions with adsorbed active ingredients can occur during application of dusts used as pesticide carriers, or from subsequent wind erosion. Emissions also may contain pesticide degradation products, which may or may not be volatile. Most pesticides, however, are sufficiently long lived to allow some volatilization before degradation occurs. Processes affecting emissions through volatilization of agricultural pesticides applied to soils or plants have been studied in numerous laboratory and field research investigations. The 3 major parameters that influence the rate of volatilization are the nature of the AI, the meteorological conditions, and soil adsorption. Of these 3 major parameters, the nature of the AI probably has the greatest effect. The nature of the AI encompasses physical properties, such as vapor pressure, Henry’s law constant, and water solubility; and chemical properties, including soil particle adsorption and hydrolysis or other degradative mechanisms. At a given temperature, every AI has a characteristic Henry’s law constant and vapor pressure. The evaporation rate of an AI is determined in large part by its vapor pressure, and the vapor pressure increases with temperature and decreases with adsorption of the AI to soil. The extent of volatilization depends in part on air and soil temperature. Temperature has a different effect on each component relative to its vapor pressure. An increase in temperature can increase or decrease volatilization because of its influence on other factors such as diffusion of the AI toward or away from the soil surface, and movement of the water in the soil. Usually, an increase in temperature enhances volatilization because the vapor pressure of the AI increases. Wind conditions also can affect the rate of AI volatilization. Increased wind and turbulence decrease the stagnant layers above a soil surface and increase the mixing of air components near the surface, thus increasing volatilization. The effects of the third major parameter, soil adsorption, depend not only on the chemical reactivity of the AI but to a great extent on the characteristics of the soil. Increased amounts of organic matter or clay in soils can increase adsorption and decrease the volatilization rate of many AIs, particularly the more volatile AIs that are nonionic, weakly polar molecules. The soil moisture content can also influence the rate of vaporization of the weakly polar AIs. When soil is very dry, the volatility of the AI is lowered significantly, resulting in a decrease in emissions. The presence of water in the soil can accelerate the 9.2.2-2 EMISSION FACTORS 1/95 evaporation of pesticides because, as water evaporates from the soil surface, the AI present in the soil will be transported to the surface, either in solution or by codistillation or convection effects. This action is called the "wick effect" because the soil acts as a wick for movement of the AI. Many materials used as inert ingredients in pesticide formulations are organic compounds that are volatile liquids or gases at ambient conditions. All of these compounds are considered to be volatile organic compounds (VOC). During the application of the pesticides and for a subsequent period of time, these organic compounds are volatilized into the atmosphere. Most of the liquid inert ingredients in agriculture pesticide formulations have higher vapor pressures than the AIs. However, not all inert ingredients are VOCs. Some liquid formulations may contain water, and solid formulations typically contain nonvolatile (solid) inert ingredients. Solid formulations contain small quantities of liquid organic compounds in their matrix. These compounds are often incorporated as carriers, stabilizers, surfactants, or emulsifiers, and after field application are susceptible to volatilization from the formulation. The VOC inert ingredients are the major contributors to emissions that occur within 30 days after application. It is assumed that 100 percent of these VOC inert ingredients volatilize within that time. Two important mechanisms that increase emissions are diffusion and volatilization from plant surfaces. Pesticides in the soil diffuse upward to the surface as the pesticide at the soil surface volatilizes. A pesticide concentration gradient is thus formed between the depleted surface and the more concentrated subsurface. Temperature, pesticide concentration, and soil composition influence the rate of diffusion. The rate of volatilization from plant surfaces depends on the manner in which the pesticide covers the plant structure. Higher volatilization losses can occur from plant surfaces when the pesticide is present as droplets on the surface. Volatilization slows when the remaining pesticide is either left in the regions of the plant structure less exposed to air circulation or is adsorbed onto the plant material. Alternative techniques for pesticide application or usage are not widely used, and those that

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